The present invention relates to a viewing device for use in verifying the authenticity of documents and other articles which are coated by a retro-reflective legend bearing layer.
A substantially transparent film material has recently become available which has both retro-reflective legend areas and retro-reflective background areas of differing reflectances. The film is substantially transparent under ordinary diffused lighting conditions, so that the legend and background areas are essentially indistinguishable, but when viewed under substantially collimated light, the legend areas and background areas are clearly distinguishable. Thus, if alterations have been made or attempted in the document or other article to which the film is attached, or if the document is not genuine, these facts will appear as irregularities or disturbances in the legend when the film is viewed under retro-reflective viewing conditions. A complete description of such a film material and its manner of use is found in Sevelin et al, U.S. Pat. No. 3,801,183, the specification and drawings of which are hereby incorporated by reference herein.
Viewing devices are known which are designed for use with such a legend bearing retro-reflective film, such as those described in Craven, U.S. Pat. No. 3,767,305 and Johnson, U.S. Pat. No. 3,767,291. A hand retroviewer is described in Johnson, U.S. Pat. No. 3,832,038. The hand retroviewer, however, is obviously limited in application and the retroviewers described in the other above mentioned patents are severely limited as to the size and shape of the film-covered document or article which can be accommodated for viewing and as to the angle of viewing. Thus, niether retroviewer can accommodate oversized or oddly shaped articles. Also, the Johnson viewer requires that the observer be standing up or sitting in an awkward position and looking almost straight down to perceive the image. Additionally, the Craven viewer requires adjustments depending upon whether the observer is standing or sitting, and the position of the viewing apparatus cannot be changed independently of the shelf holding the article to be viewed. Further, both the Johnson and Craven viewers require precise positioning of the eye or other receptor to perceive the best image.